Apparatus and methods for determining a pass/fail condition of a memory device

ABSTRACT

Memory devices including an array of memory cells, a first buffer selectively connected to the array of memory cells and corresponding to a particular bit rank of a byte of information of a programming operation of the memory device, and a second buffer selectively connected to the array of memory cells and corresponding to the particular bit rank of a different byte of information of the programming operation of the memory device, wherein an output of the first buffer and an output of the second buffer are connected in parallel to a common line, as well as methods of their operation to indicate a pass/fail condition of the programming operation.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 14/012,602, titled “PAGE BUFFER CONNECTIONS AND DETERMINING PASS/FAIL CONDITION OF MEMORIES” and filed Aug. 28, 2013 (allowed), which is a continuation of U.S. patent application Ser. No. 12/896,487, titled “MEMORY ARRAYS AND METHODS OF OPERATING MEMORY” and filed Oct. 1, 2010, now U.S. Pat. No. 8,526,238, which are each commonly assigned and incorporated herein by reference.

FIELD

The present disclosure relates generally to memories, and in particular, in one or more embodiments, the present disclosure relates to array efficiencies in memories.

BACKGROUND

Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic devices. There are many different types of memory including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), and flash memory.

Flash memory devices have developed into a popular source of non-volatile memory for a wide range of electronic applications. Flash memory devices typically use a one-transistor memory cell that allows for high memory densities, high reliability, and low power consumption. Changes in threshold voltage of the cells, through programming of a charge storage structure, such as floating gates or trapping layers or other physical phenomena, determine the data state of each cell. Common uses for flash memory include personal computers, personal digital assistants (PDAs), digital cameras, digital media players, digital recorders, games, appliances, vehicles, wireless devices, cellular telephones, and removable memory modules, and the uses for flash memory continue to expand.

Flash memory typically utilizes one of two basic architectures known as NOR flash and NAND flash. The designation is derived from the logic used to read the devices. In NOR flash architecture, a logical column of memory cells is coupled in parallel with each memory cell coupled to a data line, such as those typically referred to as digit (e.g., bit) lines. In NAND flash architecture, a column of memory cells is coupled in series with only the first memory cell of the column coupled to a bit line.

As the performance and complexity of electronic systems increase, the requirement for additional memory in a system also increases. However, in order to continue to reduce the costs of the system, the parts count must be kept to a minimum. This can be accomplished by increasing the memory density of an integrated circuit by using such technologies as multilevel cells (MLC). For example, MLC NAND flash memory is a very cost effective non-volatile memory.

Multilevel cells can take advantage of the analog nature of a traditional flash cell by assigning a bit pattern to a specific threshold voltage (Vt) range stored on the cell. This technology permits the storage of two or more bits per cell, depending on the quantity of voltage ranges assigned to the cell and the stability of the assigned voltage ranges during the lifetime operation of the memory cell.

For example, a cell may be assigned four different voltage ranges of 200 mV for each range. Typically, a dead space of 0.2V to 0.4V is between each range to keep the ranges from overlapping. If the voltage stored on the cell is within the first range, the cell is storing a logical 11 state and is typically considered the erased state of the cell. If the voltage is within the second range, the cell is storing a logical 01 state. This continues for as many ranges that are used for the cell provided these voltage ranges remain stable during the lifetime operation of the memory cell.

Since two or more states are stored in each MLC, the width of each of the voltage ranges for each state can be very important. The width is related to many variables in the operation of a memory circuit. For example, a cell could be verified at one temperature and read at a different temperature. The circuitry that determines if the cell is erased or programmed to the correct Vt range has to make that determination. That circuitry has some of its characteristics influenced by temperature. A Vt window is a sum of all of these types of differences, translating into a shift in the perceived window of the Vt. In order for the window to operate, the width of the four states plus a margin between each state should amount to the available window.

Array efficiency is one important memory parameter. The higher the array efficiency, the greater the density and capabilities of memories can be. Array efficiency is typically defined as the array area divided by the sum of the array area and the periphery area, where the array area is the total area occupied by the memory cells of the array itself, and the periphery area is the area used for supporting components of the memory. To increase array efficiency, one way is to decrease the periphery area. In MLC NAND flash memory, the biggest part of the periphery area is typically the page buffer. A typical page buffer comprises circuitry such as sense amplifiers, data latches, and a byte selector (also called a data detector). A typical data detector includes circuitry such as a column selector, a knock-out latch, and a pass/fail system. Column select is used during data loading and retrieval. Knock-out latches are used to store information about a bad column and allow its removal from verification, and the pass/fail system allows elimination of a byte from verification.

For reasons such as those stated above, and for other reasons, such as those stated below, which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for, among other things, increasing memory array efficiency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a dynamic data cache of the prior art;

FIG. 1A is a block diagram of a part of a memory device of the prior art;

FIG. 2 is a block diagram of a memory device according to one embodiment of the present disclosure;

FIG. 3 is a flow chart diagram of a method according to another embodiment of the present disclosure;

FIG. 4 is a flow chart diagram of a method according to yet another embodiment of the present disclosure; and

FIG. 5 is a functional block diagram of an electrical system having at least one memory device with a memory array configuration according to one embodiment of the present invention.

DETAILED DESCRIPTION

In the following detailed description of the embodiments, reference is made to the accompanying drawings that form a part hereof. In the drawings, like numerals describe substantially similar components throughout the several views. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the present invention.

The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present disclosure is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.

A block diagram of a simplified typical dynamic data cache 10 (DDC) is shown in FIG. 1. The DDC 10 comprises an access transistor 12 (e.g., bit line clamp) that connects the memory array to the DDC. When transistor 12 is turned on, a selected bit line is connected to the DDC. The DDC 10 further comprises a precharge circuit 14. When the an odd or even bit line is connected to the DDC 10, the precharge circuit 14 precharges that particular bit line prior to a sense operation.

A temporary data cache (TDC) 16 is used to temporarily store data during a program or sense operation. The data is stored in the TDC 16 before being moved to or after being moved from the primary data cache (PDC) 22, the secondary data cache (SDC) 24, dynamic cache (DDC1) 20, or dynamic cache (DDC2) 18. If the present operation is a sense operation, the data in the TDC 16 is moved to the I/O line 26 for use by external circuits such as a microprocessor that initiated the sense operation. If the present operation is a program operation, the data in the TDC 16 is moved to the selected memory cell during the portion of the operation in which the selected memory cell is programmed with the data.

The main data storage portion of the DDC 10 comprises a DDC2 circuit 18, a DDC1 circuit 20, a PDC circuit 22, and a SDC circuit 24. The DDC1 and DDC2 circuits 20, 18 are used for controlling programming and storing data for selected memory cells in combination with the PDC circuit 22. PDC circuit 22 may also be referred to as a page buffer, such as page buffers 106, 108 described in further detail below.

A typical NAND memory page buffer architecture is shown in FIG. 1A. Page buffers (i.e., data caches) such as buffers 106 and 108 are organized into groups of eight. Eight page buffers form a basic structure. The page buffers of this structure are connected via a common line (dvfy) 102 to a data detector circuit 104. For each structure of eight page buffers, there is a data detector circuit 104.

A typical NAND memory works by page. A page is composed of a certain number of structures such as those described (i.e., 4096 bytes represented by 4096 structures of page buffers). A page can be defined as, for example, the number of cells in a block of memory cells which are operated on by a single programming or read operation. A row of memory cells may comprise, e.g., two physical pages of memory cells, and each of those physical pages can comprise a respective two or more logical pages (e.g., an upper page and a lower page). In this manner, a single cell can store data corresponding to different logical pages. All data detectors of a page (4096 in one embodiment) are connected together. Each data detector takes up approximately 15 percent of the total structure area. The data detector logic is used to select a specific structure of eight page buffers. A pass/fail system 101 precharges the dvfy line 102, and when a cell coupled to one of the page buffers of the structure (referred to herein, by example, as a “byte” and in which a “bit” is one of the eight individual components of a byte), the entire byte is failed. Each page buffer, such as page buffers 106 and 108, comprises a latch 110, 112, a check transistor 114, 116, a program transistor 118, 120, and a sense circuit 122, 124. When a particular cell is programmed, its respective latch has a logic 0 as its output. When the particular cell of the page buffer has failed programming, (that is, not programmed), its respective latch has a logic 1 as its output.

When each page buffer that is connected to the common line indicates its respective cell has been programmed, its respective program transistors are off, so once the common line 102 is precharged, and the check transistors and sense circuits are turned on, the common line remains precharged and transistor P1 remains off. When a page buffer connected to the common line indicates its coupled cell has failed programming, the common line is discharged to ground, turning transistor P1 on, and a fail is detected. Programming continues with additional program pulses and verification until all cells are successfully programmed, or until a maximum number of programming pulses has been reached. If the byte is still failed, then it is identified as a bad byte. If the byte is identified as a bad byte, the knock-out latch 126 is set, and that byte is no longer used. Once a byte is marked as bad, that information may be stored for setting the knock-out latch on startup. Once a column is determined to be bad, the knock-out latch is set, and that removes the column from fail counting. This results in many latches that are read to determine if bytes are bad or not. This takes time and energy.

The various embodiments disclosed herein include methods and memories that can reduce the periphery area of memory arrays by eliminating elements of the data detector to allow for improved array efficiency. For purposes of this disclosure, a rank of a bit (one example of a digit) within a byte is that bit at a certain logical location within the byte. Specifically, for a first byte of eight bits identified for purposes of explanation only as bit_0, bit_1, bit_2, bit_3, bit_4, bit_5, bit_6, and bit_7, and for a second byte of eight bits identified for purposes of explanation only as bit_0, bit_1, bit_2, bit_3, bit_4, bit_5, bit_6, and bit_7, each bit_0 is identified as having the same rank. For a plurality of bits of the same identification, all bits that are identified as bit_0 within their particular byte are in the same rank within the byte.

In one embodiment of the present disclosure, a memory device 200 with improved array efficiency is shown in FIG. 2. In this embodiment, there is no data detector as is present in the prior art. Instead, operation is performed as follows. Each byte of information comprises eight bits, with representative page buffers 202 and 204 representing those bits shown. Each of the eight bits of a byte are identified, for purposes of explanation only, as bit_0, bit_1, . . . , bit_7. In this embodiment, a common line 206 is connected in parallel to each bit_0 page buffer of a page of the memory array. A respective common line is connected in parallel to each bit_1 page buffer of the page, to each bit_2 page buffer of the page, . . . , to each bit_7 page buffer of the page (each bit_7 page buffer being connected to common line 208). Each common line allows performance of a parallel operation for each page buffer by its bit rank within its byte. In this embodiment, each of the eight common lines has its own pass/fail circuit (circuits 210 and 212 shown) to determine whether its respective common line has all cells that have successfully been programmed, or has at least one cell that has failed to program successfully.

Each pass/fail circuit can be used to determine whether the common line connected to it has been discharged, and to issue an output that indicates a pass or a fail for the cells connected to the common line. For purposes of passing, an inhibited cell is considered to be passing due to its having reached its desired threshold voltage, and having a program latch set indicating that the cell is programmed. The pass/fail outputs of each of the, in this embodiment, eight pass/fail circuits, are combined in OR logic 214 in parallel for all the bytes of one page. With this combination, a determination can be made as to whether a byte is failing.

The determination of passing or failing for a byte is determined in one embodiment through the use of the OR combination of the output from the pass/fail circuits for each of the common lines. In this embodiment, a passing indication is an indication that the cell is programmed, and a failing indication is an indication that the cell has not yet been verified as programmed. The common line connecting each page buffer bit rank as described above allows the performance of a parallel operation for each bit. If each bit is passing, then the logic signal on that bit rank's common line will be 0. If all bits on each common line are passing, then the result of the OR combination of all the common lines will be 0 indicating all bits, and therefore all bytes, are passing. If any bit that is not inhibited fails, its common line will be at a logic 1 signal, and the OR combination of the common lines will be a logic 1, indicating a failing bit. Each common line, therefore, conveys through its pass/fail circuit information indicating if all of its parallel connected bits have passed.

The determination of passing or failing for a bit is determined in one embodiment through selective sensing and use of the individual pass/fail circuits. For example, the outputs of the individual pass/fail circuits can show any bit rank (i.e., bit_0, bit_1, . . . , bit_7) that has at least one bit failing. This is indicated if the common line for that bit rank is discharged on verification. By selectively inhibiting columns, a specific failing bit can be identified. Specifically, if all columns are inhibited except one, and the common line for that bit rank is discharged, the bit on the column that is not inhibited is a failing bit. That does not preclude other bits in the bit rank being failing bits as well, but does specifically identify a particular bit as failing.

Each page buffer 202, 204 has a program latch 216, 218 with an output connected to a program indicator transistor 220, 222. The program latch is selectively connected to its respective data line through use of bit line clamp transistors (see FIG. 1). The program indicator transistors 220, 222 are connected between the common line 206, 208 and check transistors 224, 226, respectively. For page buffer 202, for example, if the corresponding cell is programmed to its desired threshold voltage after a programming pulse, the latch 216 is set and outputs a logic 0 to the gate of program indicator transistor 220. When common line 206 is precharged, and verification is performed, check transistor 224 is turned on. Since program indicator transistor 220 is off, the common line 206 remains charged, the pass/fail circuit 210 for common line 206 detects that it has not been discharged, and sends a logic 0 (pass) to OR circuit 214. If instead, the cell is not programmed to its desired threshold voltage after a programming pulse, the latch 216 outputs a logic 1 to the gate of program indicator transistor 220. Upon verification after precharging the common line 206, the check transistor 224 and program indicator transistor are both turned on, and the common line 206 is discharged to ground through transistors 220 and 224. The pass/fail circuit 210 for common line 206 detects that it has been discharged, and sends a logic 1 (fail) to OR circuit 214. Any bit, therefore, that is not passing, (that is, a cell that is not yet been verified as programmed) indicates a fail of the page through the discharge of its common line, leading to a fail on its pass/fail circuit, and a fail signal at the output of the OR circuit 214.

It should be understood that the logic 0 signal presented by pass/fail circuits 210, 212 could be a logic 1 signal, and that the output of the pass/fail circuits can be combined in a different logic function to obtain the same results, without departing from the scope of the disclosure.

In operation, a memory array having the common lines such as lines 206, 208 connecting page buffers of the same rank (i.e., all bit_0 page buffers of a page) functions as is shown and discussed in the flow chart diagram of FIG. 3, with reference to FIG. 2. For programming, certain columns may be identified through testing, or through earlier discovery, that are bad, that is, are not to be used. For those columns, each are marked as bad in a register or other type of storage. Columns marked as bad are excluded from verification operations in block 302. This is accomplished in one embodiment by loading bad column data into a page buffer for the page being programmed, which inhibits those columns before a first program pulse of a series of programming pulses, and for the duration of the programming sequence.

Upon initiation of programming pulses in block 304, after a first programming pulse, some cells will have been programmed and some likely will not have been programmed, i.e., failed. A pass/fail check is performed in block 306. If all cells have been programmed, the process is complete and ends at block 312. If not, all cells that have been programmed have their respective program latches set to “pass” status at block 308, and a next program pulse is applied at block 310. The pass/fail check with a sequence of increasing magnitude programming pulses is completed until all cells have been verified as programmed.

As noted, as each cell is passed, that is, as each cell is identified through verification as passing (i.e., programmed to its desired threshold voltage), the program latch for that cell is set in block 308. To accomplish this, in one embodiment, the output of the program latch is set at a logic 0 if the cell is indicated as having been programmed. Then, for verification, the common line is precharged, and the check transistor is turned on. If the cell is programmed, the logic 0 output of the program latch keeps its program indicator transistor off, and the common line is not discharged. If the cell remains unprogrammed (i.e., failing), then the common line is discharged and cell programming failure is detected. Programming continues in this fashion until all cells are successfully programmed and indicated as passed. If a cell fails to program, then the program latch remains set at a logic 1, and the common line is discharged when its check transistor is turned on.

The pass/fail check 306 is discussed in further detail with respect to FIG. 4. For the pass/fail check process of block 306, the common lines of the page are precharged in block 402, and a verify operation is performed in block 404. The verify operation discharges one or more of the common lines if the page does not pass verification. The pass/fail status of each common line is indicated by its pass/fail circuit at block 406, and the output of the pass/fail circuits is combined in OR circuitry at block 408. In decision block 410, if the OR circuit indicates all common lines pass, process flow continues at block 312, and if the OR circuit indicates that at least one of the common lines fails, process flow continues at block 308.

FIG. 5 is a simplified block diagram of a memory device 501 according to an embodiment of the disclosure, and on which various embodiments of the disclosure can be practiced. Memory device 501 includes an array of memory cells 504 arranged in rows and columns. Although the various embodiments will be described primarily with reference to NAND memory arrays, the various embodiments are not limited to a specific architecture of the memory array 504. Some examples of other array architectures suitable for the present embodiments include NOR arrays, AND arrays, and virtual ground arrays. In general, however, the embodiments described herein are adaptable to any array architecture permitting generation of a data signal indicative of the threshold voltage of each memory cell.

A row decode circuitry 508 and a column decode circuitry 510 are provided to decode address signals provided to the memory device 501. Address signals are received and decoded to access memory array 504. Memory device 501 also includes input/output (I/O) control circuitry 512 to manage input of commands, addresses and data to the memory device 501 as well as output of data and status information from the memory device 501. An address register 514 is coupled between I/O control circuitry 512 and row decode circuitry 508 and column decode circuitry 510 to latch the address signals prior to decoding. A command register 524 is coupled between I/O control circuitry 512 and control logic 516 to latch incoming commands. Control logic 516 controls access to the memory array 504 in response to the commands and generates status information for the external processor 530. The control logic 516 is coupled to row decode circuitry 508 and column decode circuitry 510 to control the row decode circuitry 508 and column decode circuitry 510 in response to the addresses.

Control logic 516 can be coupled to a sample and hold circuitry 518. The sample and hold circuitry 518 latches data, either incoming or outgoing, in the form of analog data signals. For example, the sample and hold circuitry could contain capacitors or other analog storage devices for sampling either an incoming data signal representing data to be written to a memory cell or an outgoing data signal indicative of the threshold voltage sensed from a memory cell. The sample and hold circuitry 518 may further provide for amplification and/or buffering of the sampled signal to provide a stronger data signal to an external device.

The handling of analog data signals may take an approach similar to an approach well known in the area of CMOS imager technology, where charge levels generated at pixels of the imager in response to incident illumination are stored on capacitors. These charge levels are then converted to signals using a differential amplifier with a reference capacitor as a second input to the differential amplifier. The output of the differential amplifier is then passed to analog-to-digital conversion (ADC) devices to obtain a digital value representative of an intensity of the illumination. In the present embodiments, a charge may be stored on a capacitor in response to subjecting it to a data signal indicative of an actual or target threshold voltage of a memory cell for reading or programming, respectively, the memory cell. This charge could then be converted to an analog data signal using a differential amplifier having a grounded input or other reference signal as a second input. The output of the differential amplifier could then be passed to the I/O control circuitry 512 for output from the memory device, in the case of a read operation, or used for comparison during one or more verify operations in programming the memory device. It is noted that the I/O control circuitry 512 could optionally include analog-to-digital conversion functionality and digital-to-analog conversion (DAC) functionality to convert read data from an analog data signal to a digital bit pattern and to convert write data from a digital bit pattern to an analog signal such that the memory device 501 could be adapted for communication with either an analog or digital data interface.

During a write operation, target memory cells of the memory array 504 are programmed, for example using two sets of programming pulses as described above, until voltages indicative of their Vt levels match the levels held in the sample and hold circuitry 518. This can be accomplished, as one example, using differential sensing devices to compare the held voltage level to a threshold voltage of the target memory cell. Much like traditional memory programming, programming pulses could be applied to a target memory cell to increase its threshold voltage until reaching or exceeding the desired value. In a read operation, the Vt levels of the target memory cells are passed to the sample and hold circuitry 518 for transfer to an external processor (not shown in FIG. 5) either directly as analog signals or as digitized representations of the analog signals depending upon whether ADC/DAC functionality is provided external to, or within, the memory device.

Threshold voltages of cells may be determined in a variety of manners. For example, an access line, such as those typically referred to as word lines, voltage could be sampled at the point when the target memory cell becomes activated. Alternatively, a boosted voltage could be applied to a first source/drain side of a target memory cell, and the threshold voltage could be taken as a difference between its control gate voltage and the voltage at its other source/drain side. By coupling the voltage to a capacitor, charge would be shared with the capacitor to store the sampled voltage. Note that the sampled voltage need not be equal to the threshold voltage, but merely indicative of that voltage. For example, in the case of applying a boosted voltage to a first source/drain side of the memory cell and a known voltage to its control gate, the voltage developed at the second source/drain side of the memory cell could be taken as the data signal as the developed voltage is indicative of the threshold voltage of the memory cell.

Sample and hold circuitry 518 may include caching, i.e., multiple storage locations for each data value, such that the memory device 501 may be reading a next data value while passing a first data value to the external processor, or receiving a next data value while writing a first data value to the memory array 504. A status register 522 is coupled between I/O control circuitry 512 and control logic 516 to latch the status information for output to the external processor.

Memory device 501 receives control signals at control logic 516 over a control link 532. The control signals may include a chip enable CE#, a command latch enable CLE, an address latch enable ALE, and a write enable WE#. Memory device 501 may receive commands (in the form of command signals), addresses (in the form of address signals), and data (in the form of data signals) from an external processor over a multiplexed input/output (I/O) bus 534 and output data to the external processor over I/O bus 534.

In a specific example, commands are received over input/output (I/O) pins [7:0] of I/O bus 534 at I/O control circuitry 512 and are written into command register 524. The addresses are received over input/output (I/O) pins [7:0] of bus 534 at I/O control circuitry 512 and are written into address register 514. The data may be received over input/output (I/O) pins [7:0] for a device capable of receiving eight parallel signals, or input/output (I/O) pins [15:0] for a device capable of receiving sixteen parallel signals, at I/O control circuitry 512 and are transferred to sample and hold circuitry 518. Data also may be output over input/output (I/O) pins [7:0] for a device capable of transmitting eight parallel signals or input/output (I/O) pins [15:0] for a device capable of transmitting sixteen parallel signals. It will be appreciated by those skilled in the art that additional circuitry and signals can be provided, and that the memory device of FIG. 5 has been simplified to help focus on the embodiments of the disclosure.

A program and verify function on selected pages or the like of the memory 500 is performed as described above with respect to the structure of FIG. 2, and the methods of FIGS. 3 and 4 associated therewith.

While FIG. 5 has been described with respect to sample and hold circuitry 518, it should be understood that the control logic 516 could be coupled to data latches instead of sample and hold circuitry 518 without departing from the scope of the disclosure. Data latches latch data, either incoming or outgoing. During a write operation, target memory cells of the memory array 504 are programmed, for example using two sets of programming pulses as described above, until voltages indicative of their Vt levels match the data held in the data latches. This can be accomplished, as one example, using differential sensing devices to compare the held data to a threshold voltage of the target memory cell.

Additionally, while the memory device of FIG. 5 has been described in accordance with popular conventions for receipt and output of the various signals, it is noted that the various embodiments are not limited by the specific signals and I/O configurations described. For example, command and address signals could be received at inputs separate from those receiving the data signals, or data signals could be transmitted serially over a single I/O line of I/O bus 534. Because the data signals represent bit patterns instead of individual bits, serial communication of an 8-bit data signal could be as efficient as parallel communication of eight signals representing individual bits.

CONCLUSION

Methods of programming a memory and memories using the methods have been described that, among other things, can increase array efficiency by reducing the amount of circuitry used in the periphery of the array. Individual bit and byte failures can be detected without a data detector and knock-out latch using a plurality of common lines, one for each rank of page buffers corresponding to a page, and the combination of pass/fail circuit outputs into OR logic to determine whether all cells on a page have been successfully programmed or not.

Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof. 

What is claimed is:
 1. A memory device, comprising: an array of memory cells; a first buffer selectively connected to the array of memory cells and corresponding to a particular bit rank of a byte of information of a programming operation of the memory device; a second buffer selectively connected to the array of memory cells and corresponding to the particular bit rank of a different byte of information of the programming operation of the memory device; wherein an output of the first buffer and an output of the second buffer are connected in parallel to a common line.
 2. The memory device of claim 1, wherein the byte of information and the different byte of information are bytes of information of a same page of the programming operation.
 3. The memory device of claim 2, wherein a number of bytes of information of the page of the programming operation is greater than a number of bit ranks of those bytes of information.
 4. The memory device of claim 2, further comprising: a plurality of additional buffers selectively connected to the array of memory cells and each corresponding to the particular bit rank of a respective byte of information of the same page of the programming operation; wherein an output of each buffer of the plurality of additional buffers is connected in parallel to the common line.
 5. The memory device of claim 1, wherein the array of memory cells is arranged in rows and columns, and wherein the first buffer and the second buffer are page buffers selectively connected to columns of the array of memory cells.
 6. The memory device of claim 1, further comprising a pass/fail circuit connected to the common line.
 7. The memory device of claim 6, wherein the pass/fail circuit is configured to indicate a logic level of the common line.
 8. The memory device of claim 6, wherein a number of buffers having outputs connected to the common line is equal to a number of bytes of information of the programming operation.
 9. A method of operating a memory, comprising: performing a programming operation on a plurality of memory cells; charging a common line connected to a first buffer and to a second buffer; performing a programming verification of the programming operation on a first memory cell corresponding to a particular bit rank of a first byte of information of the programming operation and on a second memory cell corresponding to the particular bit rank of a second byte of information of the programming operation; discharging the common line to the first buffer if the first memory cell fails the programming verification and discharging the common line to the second buffer if the second memory cell fails the programming verification; and indicating a fail status of the programming operation if the common line is discharged in response to the programming verification.
 10. The method of claim 9, further comprising: inhibiting a third buffer from discharging the common line, wherein the third buffer is connected to the common line.
 11. The method of claim 10, wherein inhibiting the third buffer from discharging the common line comprises inhibiting the third buffer from connecting the common line to a ground.
 12. The method of claim 9, wherein discharging the common line to the first buffer if the first memory cell fails the programming verification and discharging the common line to the second buffer if the second memory cell fails the programming verification comprises: setting a latch of the first buffer to output a first value if the first memory cell passes the programming verification and setting the latch of the first buffer to output a second value if the first memory cell fails the programming verification; setting a latch of the second buffer to output the first logic level if the second memory cell passes the programming verification and setting the latch of the second buffer to output the second logic level if the second memory cell fails the programming verification; applying the output of the latch of the first buffer to a control gate of a first transistor between the common line and a ground; and applying the output of the latch of the second buffer to a control gate of a second transistor between the common line and the ground.
 13. The method of claim 9, further comprising for each remaining byte of information of the programming operation: performing a programming verification of the programming operation on an additional memory cell corresponding to the particular bit rank of that byte of information of the programming operation; and discharging the common line to an additional buffer corresponding to that additional memory cell if that additional memory cell fails the programming verification.
 14. The method of claim 13, further comprising: charging a second common line connected to a plurality of buffers corresponding to a different bit rank of the bytes of information of the programming operation; and for each byte of information of the programming operation: performing a programming verification of the programming operation on a memory cell corresponding to the different bit rank of that byte of information of the programming operation; discharging the second common line to a buffer corresponding to that memory cell if that memory cell fails the programming verification; and indicating the fail status of the programming operation if the second common line is discharged in response to the programming verification.
 15. A memory device, comprising: an array of memory cells; a plurality of first buffers selectively connected to respective memory cells of the array of memory cells, each of the respective memory cells corresponding to a first bit rank of respective bytes of information of a programming operation of the memory device; a plurality of second buffers selectively connected to respective memory cells of the array of memory cells, each of the respective memory cells corresponding to a second bit rank of respective bytes of information of the programming operation of the memory device; a first line commonly connected to outputs of the plurality of first buffers; a second line commonly connected to outputs of the plurality of second buffers; a first pass/fail circuit having an input connected to the first line and configured to provide an output indicative of whether the first line is discharged; and a second pass/fail circuit having an input connected to the second line and configured to provide an output indicative of whether the second line is discharged; wherein each first buffer of the plurality of first buffers is configured to deactivate a respective discharge path from the first line to a ground in response to its respective memory cell passing a program verification of the programming operation; and wherein each second buffer of the plurality of second buffers is configured to deactivate a respective discharge path from the second line to the ground in response to its respective memory cell passing a program verification of the programming operation.
 16. The memory device of claim 15, further comprising an OR logic circuit having an input connected to the output of the first pass/fail circuit and having an input connected to the output of the second pass/fail circuit.
 17. The memory device of claim 15, wherein each buffer of the plurality of first buffers and the plurality of second buffers comprises a latch having an input selectively connected to the respective memory cell of that buffer and an output connected to a control gate of a transistor in its respective discharge path.
 18. The memory device of claim 17, wherein the latch of each buffer of the plurality of first buffers and the plurality of second buffers is configured to provide its output with a first logic level if its respective memory cell passes the program verification and to provide its output with a second logic level if its respective memory cell fails the program verification, and wherein the transistor in its respective discharge path is configured to activate in response to the second logic level and to deactivate in response to the first logic level.
 19. The memory device of claim 18, wherein the transistor in the respective discharge path of each buffer of the plurality of first buffers and the plurality of second buffers is a first transistor, and wherein the respective discharge path of each buffer of the plurality of first buffers and the plurality of second buffers further comprises a second transistor between its first transistor and the ground.
 20. The memory device of claim 15, further comprising for each remaining bit rank of a byte of information of the programming operation: a plurality of additional buffers selectively connected to respective memory cells of the array of memory cells, each of the respective memory cells corresponding to a respective bit rank of respective bytes of information of the programming operation of the memory device; an additional line commonly connected to outputs of that plurality of additional buffers; and an additional pass/fail circuit having an input connected to that additional line and configured to provide an output indicative of whether that additional is discharged; wherein each buffer of that plurality of additional buffers is configured to deactivate a respective discharge path from that additional line to the ground in response to its respective memory cell passing a program verification of the programming operation. 